1. Field of the Invention
This invention relates to document feeders of the type used with an image forming apparatus such as, for example, a copying machine, facsimile machine or document storage machine. The invention includes both apparatus for and methods of document feeding.
2. Description of the Prior Art
A document feeder is generally used to feed an original document sheet (to be copied) to an image forming position on the image forming apparatus whereat the document is imaged. After imaging, the feeder removes the original document from the image forming position so that another original document can be fed to that position. Generally the image forming position is associated with an original glass plate through which the imaging occurs.
In a conventional document feeder, an original document is fed from an original feed port and positioned at a fixed image forming position on the original glass plate. A stopper arrangement is used for stopping the leading edge of an original document sheet fed in a paper feed direction when that leading edge reaches a fixed position. This stopper arrangement is designed to be movable downward by an operation mechanism provided on the main body of an image forming device so that it will not be an obstacle. After the original document has been positioned and the image forming operation is finished, the stopper arrangement is drawn in to permit the original document to exit via an exit port.
In the above discussed conventional construction, positioning is performed by defining the leading edge of the original document to be a reference and by making the stopper arrangement respond to the leading edge. A problem with such an arrangement is that the stopper arrangement becomes an obstacle to the original when it is ready to exit from the image forming position. It is necessary, therefore, to provide some mechanism for releasing the stopping arrangement at the time of exiting of the original document. Such a mechanism is complicated, resulting in operational failures. In addition, such mechanisms tend to be of large size.
As an attempted solution to this problem, a document feeder without a stopper arrangement was proposed. An original document was fed from an original document feed port, transported so that the trailing end of the original document passed a stop position on the original glass plate, and then transported in a reverse direction so that the trailing end of the original became positioned at the stop position. However, that proposed arrangement also had operational difficulties. When an original document fed from the feed port was shorter than normal, it was transported in the reverse direction before the original document already positioned at the stop position had completely exited, thereby interfering with its exit. Another operational problem occurs with longer than normal original documents. When an original is transported based on the distance where the original at the stop position is exited, the trailing end of the original may not pass the stop position if the original fed from the feed port is long.